Conventionally, to improve a communication distance, communication speed, and signal density in a server, there has been developed an optical interconnect technology for relaying communication in the server by use of an optical signal. For example, a server to which the optical interconnect technology is applied includes a unit that converts an electrical signal into an optical signal or vice versa. Such a unit that converts an electrical signal into an optical signal or vice versa converts an electrical signal indicating data to be transmitted or received into an optical signal and transmits or receives the optical signal, thereby relaying communication in the server.
As the server to which the optical interconnect technology is applied includes the unit that converts an electrical signal into an optical signal or vice versa, the number of components in the server is larger than that of a server that performs communication using an electrical signal, which results in an increase in cost. Furthermore, the unit that converts an electrical signal into an optical signal or vice versa has lower reliability than a unit using an electrical signal only. Therefore, to increase the reliability of the unit that converts an electrical signal into an optical signal or vice versa to use the converted signal in communication in the server, cost increases.
Meanwhile, there is known a technology to use an inexpensive optical device in a unit that outputs an optical signal in order to achieve the optical interconnect technology at low cost. For example, there is known a technology to apply the optical interconnect technology to a device for consumers at low cost by using a vertical cavity surface emitting laser (VCSEL) as the optical device.
Patent document 1: Japanese Laid-open Patent Publication No. 2006-067413
Patent document 2: Japanese Laid-open Patent Publication No. 2003-008136
However, the technology of optical interconnect for a consumer device, using the optical device of which the reliability is low, cannot be applied to optical interconnect for servers.
For example, a continuous operating time of a VCSEL employed in the consumer optical interconnect is set to be short; therefore, if the VCSEL is installed in a server operating around the clock, the VCSEL reaches the limitation on the operating time in a short time. Furthermore, laser output of the VCSEL employed in the consumer optical interconnect is set to high output so as to cope with a harsh environment; therefore, the progression of time-related deterioration is fast. In this manner, the VCSEL employed in the consumer optical interconnect has low reliability and therefore cannot be employed in optical interconnect for servers.